Hydroxyaromatic ethers, such as the mono-substituted hydroquinones, resorcinols and catechols are generally difficult to prepare in high purity due to the complex separation of mono-, di- and unsubstituted dihydroxybenzenes. In traditional attempts to minimize this problem, low conversions are required. As a result, the cost of manufacturing the desired product is raised.
Hydroxyaromatic ethers are well known as polymerization inhibitors and as antioxidants. The monomethyl ether of hydroquinone is of significant economic importance. Additionally, the use of compounds such as methyl 2-(4-hydroxyphenoxy)propionate has been described in the patent literature as a building block to prepare a wide range of biologically active materials, especially herbicides. See, for example, European Patent No. 483 and British Patent Specifications Nos. 1,599,121 and 1,550,574.
U.S. Pat. No. 3,976,702 discloses the preparation of phenolic compounds, having from one to five alkyl substituents, via reacting the corresponding alkyl-substituted, formylbenzene with hydrogen peroxide in the presence of a solvent and a large amount of hydrofluoric acid at a temperature of from -50.degree. C. to 50.degree. C. in order to form an intermediate formyloxybenzene which is then heated in the presence of water to give the corresponding alkyl-substituted phenolic compounds. Similarly, U.S. Pat. No. 4,051,318 discloses the preparation of alkyl-substituted formyloxybenzenes, having lower alkyl substituents via reacting the corresponding alkyl-substituted formylbenzenes with certain carboxylic peracids in the presence of a solvent and a large amount of hydrofluoric acid at a temperature of from -50.degree. C. to about 50.degree. C.
The prior art does not disclose oxidation of substituted acylaromatic compounds where one or more of the substituents are not lower alkyl. Furthermore, the prior art does not disclose the use of only catalytic amounts of a strong acid. Instead, greater than stoichiometric amounts of hydrofluoric acid are specified. In view of these deficiencies, it would be desirable to have a process for the oxidation of substituted acylaromatic compounds having substituents which are different than lower alkyl so that, for example, hydroxyphenyl ethers could be produced. Additionally, it would be economically desirable to have a process which did not require large excesses of hydrofluoric acid.